If you could go back to the late Precambrian, would you recognize these as ancestors of modern life?

This is a depiction of
Dickinsonia costata
, a member of the Ediacara fauna. No one knows quite how to categorize these organisms. Some scientists think that they are the ancestors of modern life. But most scientists believe that the Ediacara fauna died out and that other organisms were the ancestors of modern life. If you could go back in time maybe you could figure it out. But since that isn't possible, is there any way to really know?

Life Gets More Complex

Eukaryotes evolved about 2 billion years ago. Unlike prokaryotes,
eukaryotes
have a cell nucleus. They have more structures and are better organized. Organelles within a eukaryote can perform certain functions. Some supply energy; some break down wastes. Eukaryotes were better able to live and so became the dominant life form. You can see an example of a eukaryotic cell below (
Figure
below
).

A eukaryotic cell. This one is from an animal.

Multicellular Life Originates

For life to become even more complex, multicellular organisms needed to evolve. Prokaryotes and eukaryotes can be multicellular.

Toward the end of the Precambrian, the Ediacara fauna evolved (
Figure
below
). The Ediacara fauna was extremely diverse. The organisms appeared after Earth defrosted from a worldwide glaciation. The Ediacara fauna seems to have died out without leaving descendants. Other multicellular organisms appeared in the Phanerozoic.

A fossil of an Ediacara organism.

Summary

Eukaryotic cells have a nucleus. They also have well-developed structures.

Eukaryotes did not evolve until 2 billion years ago.

Ediacara organisms probably went extinct. Other organisms were the ancestors to modern life.